In modern audio playback systems individual audio sources can be located in space by the use of a plurality of loudspeakers.
In principle there are two different playback concepts for this purpose. In the conventional surround-sound systems which are usual in the cinema and home entertainment sector, the location and space information is already mixed during the audio mixing operation into individual channels to be transmitted separately, and with a playback system consisting of a plurality of loudspeakers the individual channels are played back. In this case the reproducing loudspeakers must be placed at a position relative to the listener predetermined according to the recording in order to achieve an impression of space.
More advanced systems for stereo simulations generate the control signals for the individual loudspeakers only during the reproduction, based upon position information of a sound source with respect to the playback space and the space information of a playback environment to be simulated. The systems are based on the wave field synthesis (WFS). This involves a three-dimensional audio playback process for generating virtual acoustic environments. In this case wavefronts emanating from a virtual point are generated, of which the acoustic location is not dependent upon a listener's position. The WFS is based on the Huygens principle, according to which each wavefront may also be regarded as a superimposition of elementary waves. Thus any wavefront can be synthesised from these elementary waves. For this purpose, by further means a computer program controls individual loudspeakers arranged around the listener for sound wave generation at exactly the time at which a virtual wavefront would have run through its point in space.
The mathematical basis for this is the Kirchhoff-Helmholtz integral. This states that the sound pressure is determined at every point within a source-free volume if the sound pressure and sound particle velocity are determined at all points on its surface. Thus every sound field can be reconstructed if the sound pressure and sound particle velocity are reconstructed on all points on the surface of the volume. For this purpose, however, the entire surface of the volume, that is to say all walls, ceilings and preferably floors of the playback space would have to be equipped with closely packed sound generators. Furthermore all sound generators, with their respective signal, would have to be individually controlled. In addition the space would have to be completely soundproof in order to meet the condition of the source-free volume.
Thus three-dimensional audio playback systems based on wave field synthesis produce an impression of natural and spatial sound with the aid of many loudspeakers disposed close together. Because of the high requirements with regard to space, number of loudspeakers and computing power, as a rule only proprietary systems produced, which may be appropriate only for a dedicated application (for example extension of the echo time). Furthermore conventional systems have dedicated components for signal transmission, directional processing and spatial processing, which may lead to significantly higher system latencies and to a high system price. In addition various A/D and D/A conversions can have poorer signal-to-noise ratios.
A method for controlling a sound reproduction system which is designed in order to produce an impression of spatial sound is known from EP 1 878 308 B1. In this connection a very large number of loudspeakers disposed adjacent to one another (a so-called loudspeaker array) is used for one listener. In this case the orientation of the loudspeakers is 360° in a horizontal arrangement. However, this method may need a very large number of loudspeakers and dedicated hardware.
A system for simulating spatial sound is provided, which can operate with a reduced number of loudspeakers and without dedicated components and/or proprietary hardware, and a plurality of different functions, such as extension of the echo time and directional acoustic irradiation.
This object is achieved by a system for simulating spatial sound with the features of Claim 1. Advantageous embodiments and modifications of the disclosure are described in the subordinate claims.
A system for simulating spatial sound is provided, which may include the following:                a core module with a stereo simulation module simulation module, an echo module and an interface module,        a control module,        a digital audio delay matrix module and        a digital audio/network system.        
Thus, a plurality of audio signals can be reproduced with regard to amplitude and time with a system latency less than 2.5 ms by means of a plurality of loudspeakers. In this case the system latency encompasses the complete system, from the sound source to the loudspeaker, that is to say also the amplifier, I/O modules, equaliser, signal converter, etc. On the basis of the limited latency period of <2.5 ms the system is significantly easier to handle, in particular when measuring in relation to feedback. In this case, the limited latency period is a prerequisite in order also to provide directional acoustic irradiation in addition to echo or extension of echo. The substantial superiority of this system comes to light primarily in live performances, where synchronicity between the audio signal and the gestures of the actor plays an important role. Furthermore, actors moving in the sound field of the loudspeaker are not perceived as their own echo, as in the case of a system subject to latency.
The core module controlled by the control module has a synthetic echo module for generating a synthetic echo and a regenerative echo module for generating a regenerative echo. In this connection the synthetic echo can be mixed as required with the regenerative echo. The regenerative echo module is also controlled inter alia by microphones.
The echo or the extension of the echo time and the directional acoustic irradiation in the core module are brought together or merged sequentially or simultaneously.
Furthermore the digital audio/network system may include:                a ceiling-mounted loudspeaker and        a wall-mounted loudspeaker,wherein the loudspeakers are oriented substantially horizontally in bands and the horizontal distance between the loudspeakers is substantially less than or equal to 1.5 m relative to one another. In this case this distance is measured from diaphragm center to diaphragm center. In addition the vertical position of the front and wall-mounted loudspeakers is located slightly above the audience. Thus a representative auditory impression is already achieved in a region (sweet spot) from a distance of likewise 1.5 m from the loudspeaker. With a reduced distance or with half the distance of the loudspeakers from one another of 0.75 m, the sweet spot is significantly increased, so that a representative sound experience is already achieved from 0.75 m. In this way the virtual sources can be located better and thus make a clearer impression. Moreover the focus effect of the sources is improved. Furthermore the listener feels as though he is in the virtual sound environment. If the distance of the loudspeakers from one another is increased and thus the number of loudspeakers is reduced, then effects such as audience area, location, focus and enclosure are also reduced.        
In this case the loudspeakers can be oriented on a rectangular, rhomboid or honeycomb matrix.
The ceiling-mounted loudspeakers (33c) can be oriented on a logarithmic matrix R1 extending in a longitudinal direction of a space (50).
Furthermore, the digital audio/network system may have an I/O module and an amplifier module by which a plurality of loudspeakers can be controlled. With a large number of amplifier modules and I/O modules, in particular up to 512 loudspeakers can be simultaneously controlled individually.
The system for simulating spatial sound may have a tracking system which includes a geodata transmitter and a geodata receiver, by which the position of a sound source in live operation is ascertained and delivered to the control module for conversion.
By means of the tracking system real movements and/or virtual movements can be converted with the system for simulating spatial sound and made audible for the audience.
Due to the configuration of the core module, and thus of the digital audio/network system by means of CAD software, spaces which are treated acoustically so as to have a short echo time and thus good intelligibility of speech, in particular by use of a preset, may have the acoustic attributes for example of a concert hall. Because of the CAD module and the presets the system can be freely scalable and applicable to spaces of all possible sizes and shapes as well as surfaces. Even in the case of greatly split spaces, it is possible to compensate for sound reflections. Symmetry of space is not a prerequisite here. In this case the sound characteristics of a space is simulated and calculated on the basis of the geometric conditions and/or the surface properties, such as for example sound reflection behaviour.
The system for simulating spatial sound may have an open network topology and as a result can be quickly installed and uninstalled. Thus the system can be used both in a fixed installation, for example in a concert hall, and also as a mobile installation at festivals and for example large events. Furthermore, as a result the setting up and dismantling is simplified and thus leads to a saving of time and cost.
By means of acoustic panels and/or acoustic wall parts it is possible in an acoustically inadequate environment to prevent sound from being reflected and/or to prevent the production of echo chambers which cannot be monitored. For this purpose the acoustic panels and/or acoustic wall parts are appropriately positioned in an acoustically inadequate environment. In this case both passive and also active (anti-noise) panels are used. These may have for example a passive sound insulation at certain points.
The system for simulating spatial sound can be used for production of a playback space which corresponds to the generating space acoustically, in particular in the reverberation characteristics. As a result for example a sound characteristic in a building with a long echo, for example a church, in an environment with a short echo, for example an open-air site, can be simulated and vice versa.